It's technically feature-complete, but there will likely be some changes, bugfixes and optimisations.
Right now, I really want as much feedback as possible, as not much will change post-beta
Feedback could be additional features, ways to make it simpler or faster to use.
You should definitely report any bugs you find - In some cases, this may need you to send me the .mmod file for testing. I want this to work as well as possible, after all.
There is currently no written documentation - this will be completed once out of beta. In the meantime, the Basic Setup and Usage Guide should help.

This is the MaddeModelKit - Export rigged, animated models from Blender and use them directly in GameMaker! Written in pure GML, the system is as cross-platform as GameMaker itself.
This is currently the ONLY 3D animated model system I know of that exports straight from Blender and imports directly into GameMaker, simplifying the process of model creation and iteration massively.
Models are animated by shader, to keep load off the GPU.

Included is:
An extension filled with functions to load, delete and drive models.
A pair of default shaders (MMK_ES_skin + MMK_HLSL_skin) used to drive models and correct UVs with simple data and rendering. Use this shader as a base for other materials!
A Blender export script used to create the models compatible with GameMaker. (AdvancedModelExport_V1_0_26.py in included files)
A demo material

The system currently supports:
Meshes (Position, Normal, Colour, TexCoord, Tangent+Bitangent, blendweights)
Armatures (Up to 255 bones, but meshes can only be influenced by a maximum of 64 - this is shader dependent)
Object animations
Armature animations

I've constructed a sort of material system using scripts for this too. This will be explained in the video guide.
I encourage people to create their own shaders and materials compatible this system and share them with the community!

SPECIAL NOTES FOR HTML5:
While loading models and rendering meshes works, there's a bug with armatures related to GameMaker bug 28850.

The system is otherwise tested working on:

Windows (VM/YYC)

Android (VM/YYC)

Max OSX (VM/YYC)

iOS (VM/YYC)

As Mac works, it is likely Linux works. I just don't have a machine set up to properly test this though. I do not own UWP to test those platforms, but they should work since Windows works and they're both DX11 targets.

Of course, you're free to use this system in any project, commercial or personal, as long as you don't redistribute the code. Woo.